In addition to his day job as Woot's full-time "Debunker," Jeopardy! wunderkind Ken Jennings moonlights as an author of books, and this month he has a new one in stores. It's the fifth in his Junior Genius series, this time chock-full of amazing facts about The Human Body. To mark the occasion, he'll spend all of February debunking anatomical anachronisms and medical misinformation for us. Finally: the inside scoop about our own insides.
The Debunker: Does Lactic Acid Make Your Muscles Tired?
If you ever went to a gym- or a gym class - in the late 20th century, you probably heard this helpful exercise "fact": the reason why muscles get sore and give out, my fifth grade P.E. teacher assured us, is a chemical called lactic acid. Yup, the same stuff that makes sour milk sour and yogurt yogurt-y. It's in the body as well, and when it's produced by active muscles, it eventually causes fatigue and then soreness. Burning, overworked muscles were a sign of lactic acid building up, a warning sign from your body that you need to dial it back a bit.
Weirdly, by the time gym coaches were telling us stuff like this in the 1980s and 1990s, the lactic acid theory had already been discredited for decades! What happened was this: in a series of experiments around 1920, German scientist George Meyerhof ran electricity through the leg muscles of a dead frog, to study the chemistry involved. Lactate ions were produced in the muscle when it jerked, and Meyerhof won a Nobel Prize for his discoveries about glycolysis and metabolism. For decades, scientists and exercise gurus alike assumed that lactic acid was a wasteful byproduct of muscle movement, something to be avoided.
But in the 1960s, when physiologist George Brooks heard this old canard from a track coach, he was unable to prove it in the lab. When he gave lactic acid to lab rats, in fact, he discovered that "they burned it faster than anything else." Meyerhof and others had mistaken correlation for causation. Lactic acid isn't a waste product of exercise, but a helpful fuel. It's actually there powering the muscles. We now know that when muscles give out after prolonged exercise, it's mostly due to a shortage of metabolism-powering molecules like glycogen and ATP. So when you get tuckered out at the gym or on the track, quit blaming lactic acid. It's your friend. You need it on that wall.
Quick Quiz: Leucine, lysine, and methionine are the three of the nine types of what acids that are called "essential" to your body?
Ken Jennings is the author of six books, most recently his Junior Genius Guides, Because I Said So!, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at ken-jennings.com or on Twitter as @KenJennings.